1. Field of Invention
The present invention relates to a multiplexing communication system suitable for a mobile multiplexing communication system in which a code-dividing multi-access method is applied as a multiplexing method, such as a personal communication system (PCS), a digital cellular system or the like.
2. Description of Related Art
The following publications introduce conventional techniques related to such a communication system.                1. Mobile Station—Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, IS-95;        2. CDMA—Principles of Spread Spectrum Communication, Andrew J. Viterbi, Addison Wesley, 1995; and        3. NTT DoCoMo Technical Journal Vol. 4, No. 3.        
In Publication 1, a transmission method for a plurality of series of data used in CDMA communication is provided. In Publication 1 describes a transmitter that takes a portion of the power control data for each mobile station and transmits it on a communication channel in a multiplexed manner. The transmitter assigns the connection control data to frames of transmission audio data. It is noted that the transmitter described in Publication 1 uses a part of one data region corresponding to 168 bits for audio data and uses the remaining part of the same region for connection control data.
The method of distributing audio data and connection control data in a single data region is determined based on the transmission rate of the audio data. Assuming the transmission rate is 9600 bits per second (bps), there are five distribution methods: a method in which only the audio data is transmitted; a method in which each of the audio data and the connection control data constitutes a half of the transmission data; a method in which the audio data and connection control data constitute ¼ and ¾ of the transmission data, respectively; a method in which the audio data and the connection control data constitute ⅛ and ⅞ of the transmission data, respectively; and a method in which only the connection control data constitute all of the transmission data. In these five distribution methods, the number of audio data bits and the number of connection control data bits in each frame are 168 and 0; 80 and 88; 40 and 128; 16 and 152; and 0 and 168, respectively. By using these five methods, i.e., frame formats, the audio data and the connection control data are transmitted while the transmission of the connection control data is adjusted based on the amount of information included in the audio data.
Publication 2 provides an example of transmission power control. In the communication system described in Publication 2, open-loop power control is performed based on the output of an automatic gain control circuit (hereinafter, referred to as an AGC circuit). Also, closed-loop power control is performed so as to adjust the transmission power level in response to instructions from another communication station to adjust the transmission power level. More specifically, the aforementioned method of power control is described as a method of power control for reverse-link data. In this method of power control for reverse-link data, a mobile station increases and decreases the transmission power level in response to power control bits “0” and “1”, respectively, that are sent from a base station.
As described above, in the CDMA communication systems described in each of Publications 1 and 2, both the audio data and the connection control data are logically mapped on the same physical frame, and open-loop power control and closed-loop power control are performed for the same physical frame.
Therefore, in a case where the audio data, which is called the first data, is required to have a communication quality different from that of the connection control data, which is called the second data, transmission power control has to be performed so as to achieve the higher of the two communication qualities.
In addition, Publication 1 provides that first and second audio data are transmitted instead of audio data and connection control data.
Publication 3 describes a high-speed transmission technique, which uses orthogonal symbol channels. In this transmission technique, a data series having a higher transmission rate is transmitted using a plurality of physical channels that are divided by orthogonal symbol channels. In this transmission technique, single path power control is performed for the plurality of physical channels, because the plurality of physical channels carry data having the same quality.
However, when there are a plurality of series of logical data with different required qualities, in order to transmit physical data obtained from the plurality of series of logical data, a new power controller is required in order to achieve all the required qualities while preventing excessive power transmission.
In the case of a data series for which re-try operation is not performed, such as telephone call data, when the required quality of the data series is not achieved, noises may interfere with the data. In this case, the audio content of the telephone call is not correctly judged at the receiver end. In the case of a data series for which re-try operation is performed, such as connection control data, when the required quality is not achieved, overhead due to the re-try operation may be large, thereby decreasing the transmission rate. Thus many problems may arise when the required qualities of any of the data series is not achieved.
On the other hand, if excessive power transmission is permitted in a CDMA communication system, the excessive power may interfere with communication between other users, leading to a decrease in the number of simultaneous connections possible at one base station. Such interference accounts for most of the noise occurring in communication signals between other users.